1. Field
The present invention relates to a wireless power transmission technique using magnetic resonance, and more particularly to an apparatus for transmitting magnetic resonance wireless power using higher order mode resonance, a receiving terminal, and a method for transmitting and receiving wireless power using the same, which are suitable to overcome efficiency deterioration due to the basic characteristics of the existing magnetic resonance type wireless power transmission.
2. Description of Related Art
In general, magnetic resonance type wireless power transmission is preformed in a manner that a transmission device generates a frequency signal that corresponds to a basic mode resonance of a resonator and transfers the generated frequency signal to the resonator to wirelessly transfer electric power. In this case, in order to increase the signal generation efficiency of the transmission device, the transmission device is configured to have an inverter or switching amplifier structure.
In such an inverter or switching amplifier structure, the basic output waveform in a time domain appears in the form of a square wave, and according to this square wave signal, about 85% of the overall power appears in a basic mode resonance frequency and the remaining power appears in a higher mode resonance frequency signal. According to an existing method for transmitting magnetic resonance type wireless power, the basic mode resonance frequency signal of the resonator is transferred with high efficiency, but the higher mode resonance frequency signal has very low transmission efficiency. Accordingly, only the basic mode resonance frequency component of the transmission device signal is transferred with high efficiency, but the higher mode resonance frequency signal is unable to be transferred well.
FIG. 1 is a block diagram illustrating the configuration of a typical apparatus for transmitting magnetic resonance type wireless power. The apparatus for transmitting magnetic resonance type wireless power in the related art includes a transmitter 102, a transmission resonator 104, a reception resonator 106, and a receiver 108.
Referring to FIG. 1, the transmission resonator 104 and the reception resonator 106 of the apparatus for transmitting wireless power in the related art can transfer the basic mode frequency signal of each resonator with high efficiency, but the transfer efficiency of the higher mode frequency signal is very low. Accordingly, the existing system for transmitting magnetic resonance type wireless power has evolved in the direction to improve the efficiency of the basic mode frequency signal.
FIG. 2 is a characteristic graph showing the transfer characteristics between the existing magnetic resonance type transmission resonator and the reception resonator.
Referring to FIG. 2, according to the transfer characteristics between the existing magnetic resonance type transmission resonator 104 and the reception resonator 106, the basic mode resonance frequency of 1.79 MHz has a value of about −1.0 dB, the third-order mode resonance frequency of 5.4 MHz has a value of about −70.1 dB, and the fifth-order mode resonance frequency of 8.82 MHz has a value of about −41.0 dB. According to the transfer characteristics between the existing magnetic resonance type transmission resonator 104 and the reception resonator 106 as described above, high transfer characteristics appear at the basic mode resonance frequency, and lower transfer characteristics appear at the higher mode resonance frequencies.
FIGS. 3A and 3B illustrate a waveform of a square wave, which is an output waveform of a general high-efficiency transmitter, in a time domain and a waveform of the square wave in a frequency domain. Referring to FIGS. 3A and 3B, the time-domain waveform of the square wave appears to be repeated for a predetermined period, and the frequency-domain waveform of the square wave appears to be generated for the basic mode and the odd-numbered high-order modes as expressed in Equation 1 below.
                              x          ⁡                      (            f            )                          =                              1            2                    +                                    2              π                        ⁢                          cos              ⁡                              (                                  f                  0                                )                                              +                                    2                              3                ⁢                                                                  ⁢                π                                      ⁢                          cos              ⁡                              (                                  3                  ⁢                                                                          ⁢                                      f                    0                                                  )                                              +                                    2                              5                ⁢                                                                  ⁢                π                                      ⁢                          cos              ⁡                              (                                  5                  ⁢                                                                          ⁢                                      f                    0                                                  )                                              +                                    2                              7                ⁢                                                                  ⁢                π                                      ⁢                          cos              ⁡                              (                                  7                  ⁢                                                                          ⁢                                      f                    0                                                  )                                              +                                    [                  Equation          ⁢                                          ⁢          1                ]            
If power rates by modes in the frequency domain of the square wave is calculated through multiplication of respective coefficients of the basic mode frequency and the higher mode frequencies of the square wave expressed in Equation 1 above, about 85% of power appears at the basic mode frequency, about 9.5% of power appears at the third-order mode frequency, about 3.4% of power appears at the fifth-order mode frequency, and about 0.02% of power appears at the seventh-order mode frequency.
As shown in FIGS. 3A and 3B and expressed in Equation 1, if the square wave, which is an output waveform of the general high-efficiency transmitter, is transmitted using the existing magnetic resonance method, only 85% of the overall power can be transferred. This causes the power transfer efficiency of the whole system to be lowered and waste of energy to occur.